Heretofore, such a mandrel for a vertical-type pipe expanding apparatus is arranged as shown in FIG. 6, for example. A plurality of holes 17 are bored in the lower portion of a reciprocating member 16 of the vertical-type pipe expanding apparatus, and mandrels 18 have their heads 19 fitted into the holes 17. Hard balls 22 or the like being urged by springs 21 are engaged in recessed grooves 20 formed in advance around the heads 19, respectively, whereby the mandrels 18 are locked in place so as to extend vertically downwardly from the reciprocating member.
In such a vertical-type pipe expanding apparatus 23 provided with the mandrels 18 locked to and vertically downwardly extending from the lower portion of the reciprocating member 16, the desired pipe expanding operation is performed as follows. As shown in FIG. 7, when a cylinder 24 mounted at the top of the vertical-type pipe expanding apparatus 23 is extended and contracted, the reciprocating member 16 is forced to move in the vertical direction correspondingly. Upon the downward movement of the reciprocating member 16, tip ends of the mandrels 18 are inserted into pipes 25 to be expanded under pressure, which pipes are previously set below the reciprocating member 16. As a result, the outer diameter of each pipe 25 is increased or expanded so as to fixedly connect the pipes 25 and fins 26, through which the pipes have been previously inserted in place, to each other under pressure.
However, the conventional mandrel for the vertical-type pipe expanding apparatus described above has suffered from the problems as follows.
With the above conventional mandrels, when the number and/or positions of the pipes to be expanded are changed, the number and/or positions of the mandrels attached to the reciprocating member must be modified in accordance with the change intended.
In the prior-art arrangement, therefore, whenever an array pattern of the pipes to be expanded is changed, there occurs the need of removing and attaching a large number of mandrels to rearrange them as required.
In the case of performing such rearranging work of the mandrels, the operation of replacing the mandrels for each row or column is very troublesome and time-consuming, which results in the very poor operability.
Furthermore, although the conventional mandrel utilizes, as locking means, one or more hard balls being urged by the springs for the purpose of facilitating the removing and attaching work of the mandrels, the number of those balls and springs is required to be at least equal to the total number of mandrels attached. This results in the problems of extremely complicating the structure, increasing difficulties in the manufacturing, and raising the production cost.